TCAS II communicate?

[CitationTen]

Hi,

Just wondering if anyone can tell me whether or not TCAS II units communicate with each other in a RA situation. ie - The TCAS II in aircraft A tells the aircraft to climb, and in turn sends this signal to aircraft B (that aircraft A is climbing), and as a result, the TCAS II in aircraft B tells aircraft B to descend.

Just curious because someone told me they do "communicate" with each other, but haven't been able to verify any of this in any manuals. Does anyone know the answer to this for certain? Thanks for any insight!

Cheers

[esreverlluf]

Yep they do communicate - mainly to ensure that two conflicting aircraft aren't both issued with the same RA by their respective TCAS units.

Example - Interlaken, had both aircraft obeyed their TCAS RAs, the accident was probably avoidable.

[AerocatS2A]

From Wikipedia: (http://en.wikipedia.org/wiki/Traffic_Collision_Avoidance_System#TCAS_II)

TCAS II systems coordinate their resolution advisories before issuing commands to the pilots, so that if one aircraft is instructed to descend, the other will typically be told to climb — maximising the separation between the two craft.

[Tarq57]

Example - Interlaken, had both aircraft obeyed their TCAS RAs, the accident was probably avoidable.

Does this refer to the B757/Tu154 at Uberlingen? Or yet another nasty?
I'm unfamiliar with the Interlaken reference.

[TheGorrilla]

Indeed they do. I hear that the TCAS 2 units talk to each other and work out the best escape in the vertical plane for both aircraft based upon the available performance. Present flight path is also taken into account along with relative position.

[esreverlluf]

Markjoy - we are talking about the one and the same accident.

[Tarq57]

Thanks. Note to self: Must google Interlaken...

[Jaguar Pilot]

The RAs are then known as coordinated RAs.

The system requires the installation of SSR Mode S on both aeroplanes.
Mode A does not have the capability.